The present invention relates to a composite container having a barrier property, particularly to a composite container which has a good barrier property and a sufficient strength, and is capable of being produced at a low cost without complicating the production process to be used therefor.
Hitherto, when a composite container which is required to have a gas barrier property is produced, there has generally been used a production process wherein the packaging material for constituting such a container is caused to have a laminate structure, and a layer of an aluminum foil is disposed or interposed in the laminate structure. In addition, such a container is generally disposable, i.e., is thrown away after a single use thereof.
However, it has recently been required that the resources (or natural resources) are to be recycled. From such a viewpoint, there has been demanded a container which is capable of being collected after the use thereof and being separated into the respective materials constituting the container so that the thus separated materials can be recycled or reused. However, in the case of the conventional container formed from the packaging material as described above using the aluminum foil, there has been posed a problem such that the aluminum foil disposed or laminated between the layers of resins or papers cannot be easily separated and collected.
In order to solve such a problem, there have been developed containers of various types which have a good barrier property without using a metal thin film such as an aluminum foil. For example, Japanese Laid Open Patent Application (JP A, KOKAI) No. 22624/1988 discloses a container which is formed from a packaging material having a five layer structure comprising a polyethylene (PE) resin layer/a paper layer/a PE resin layer/a nylon 6 layer/and a PE resin layer disposed from the inner side of the container; Japanese Laid Open Patent Application No. 312143/1988 discloses a container which is formed from a packaging material having a five layer structure comprising a polyethylene (PE) resin layer/a paper layer/a PE resin layer/an ethylene-vinylalcohol copolymer (EVOH) layer/and a PE resin layer disposed from the inner side of the container; Japanese Laid Open Patent Application No. 160551/1990 discloses a container which is formed from a packaging material having a six layer structure comprising a polyethylene (PE) resin layer/a paper layer/a PE resin layer/an EVOH layer/a nylon 6 layer/and a PE resin layer disposed from the inner side of the container; etc.
However, among these conventional containers, the first container as described above has a problem such that the Nylon 6 layer only provides an insufficient gas barrier property. Further, in the case of the second container as described above, the EVOH layer may provide a good barrier property but it does not have a sufficient strength. In addition, when such a container is used as one for containing a soft drink, since the EVOH layer may take up water and the barrier property of the EVOH layer may extremely decrease when the EVOH layer contacts such a content, it is required to subject the end surface disposed inside of the container to a treatment such as skiving so that the EVOH layer may be covered with another material. As a result, the second container has a problem such that it requires a complicated production process. Further, in the case of the third container as described above, since the substrate material layer is disposed outside the EVOH layer and the nylon 6 layer, the container can have both of an excellent barrier property and a sufficient strength but it requires a higher production cost because it has both of the EVOH layer and the nylon 6 layer.
On the other hand, in a case where a pouring member is mounted the above composite container having a barrier property, it has been used a method wherein a pouring member, e.g., comprising a polyolefin resin such as polyethylene is inserted into an opening formed in the main body of the composite container so that it is penetrated from the inner side of the main body of the composite container, and a flange portion of the pouring member is fixed to the inner peripheral surface of the main body of the composite container.
In the case of the conventional composite container having such a pouring member mounted thereto, when the polyolefin type resin layer is formed at the time of the production of the laminate sheet as a material constituting the container, or when the container is formed from the laminate sheet, the polyolefin type resin is subjected to pyrolysis to produce a volatile component such as aliphatic hydrocarbons. Therefore, such a container has a problem such that the volatile component may migrate to the content such as an orange juice contained in the container so that the taste of the content may be changed or an odor is imparted to the content; or the flavor or taste of the content is impaired because the polyolefin type resin layer constituting the inner peripheral surface layer is liable to adsorb or transmit the flavor component of the content such as the orange juice.
From such a viewpoint, there has been investigated or researched, as a composite container which is excellent in a flavor component retaining property, a composite container wherein the inner layer comprises a layer of a semi-aromatic polyamide resin which is a copolymer comprises an aromatic polyamide forming component comprising an aliphatic diamine and isophthalic acid and/or terephthalic acid; and an aliphatic polyamide forming component comprising a lactam or an aliphatic diamine and an aliphatic dicarboxylic acid.
However, according to the present inventor's investigation, when a pouring member comprising an integrally molded member comprising a polyolefin type resin such as polyethylene is intended to be applied or mounted to such a composite container having a flavor component retaining property, a sufficient adhesion property between the container and the pouring member has not been obtained.